Initial support for histograms (eg. cumulative stats)

1 files changed, 121 insertions, 0 deletions

diff --git a/util/histogram.cpp b/util/histogram.cpp
new file mode 100644
index 00000000000..45bc9a8ddd2
--- /dev/null
+++ b/util/histogram.cpp
@@ -0,0 +1,121 @@
+// histogram.cc
+
+/**
+*    Copyright (C) 2010 10gen Inc.
+*
+*    This program is free software: you can redistribute it and/or  modify
+*    it under the terms of the GNU Affero General Public License, version 3,
+*    as published by the Free Software Foundation.
+*
+*    This program is distributed in the hope that it will be useful,
+*    but WITHOUT ANY WARRANTY; without even the implied warranty of
+*    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+*    GNU Affero General Public License for more details.
+*
+*    You should have received a copy of the GNU Affero General Public License
+*    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include <limits>
+#include <sstream>
+#include <iomanip>
+
+#include "histogram.h"
+
+namespace mongo {
+
+    using std::ostringstream;
+    using std::setfill;
+    using std::setw;
+
+    Histogram::Histogram( const Options& opts ) 
+        : _initialValue( opts.initialValue )
+        , _numBuckets( opts.numBuckets )
+        , _boundaries( new uint32_t[_numBuckets] )
+        , _buckets( new uint64_t[_numBuckets] ){
+
+        // TODO more sanity checks
+        // + not too few buckets
+        // + initialBucket and bucketSize fit within 32 bit ints
+
+        // _boundaries store the maximum value falling in that bucket.
+        _boundaries[0] = _initialValue + opts.bucketSize;
+        for ( uint32_t i = 1; i < _numBuckets - 1; i++ ){
+            _boundaries[i] = _boundaries[ i-1 ] + opts.bucketSize;
+        }
+        _boundaries[ _numBuckets-1 ] = std::numeric_limits<uint32_t>::max();
+
+        for ( uint32_t i = 0; i < _numBuckets; i++ ) {
+            _buckets[i] = 0;
+        }
+    }
+
+    Histogram::~Histogram() {
+        delete [] _boundaries;
+        delete [] _buckets;
+    }
+
+    void Histogram::insert( uint32_t element ){
+        if ( element < _initialValue) return;
+
+        _buckets[ findBucket(element) ] += 1;
+    }
+
+    string Histogram::toHTML() const{
+        uint64_t max = 0;
+        for ( uint32_t i = 0; i < _numBuckets; i++ ){
+            if ( _buckets[i] > max ){
+                max = _buckets[i];
+            }
+        }
+        if ( max == 0 ) {
+            return "histogram is empty\n";
+        }
+
+        // normalize buckets to max
+        const int maxBar = 20;
+        ostringstream ss;
+        for ( uint32_t i = 0; i < _numBuckets; i++ ){
+            int barSize = _buckets[i] * maxBar / max;
+            ss << string( barSize,'*' ) 
+               << setfill(' ') << setw( maxBar-barSize + 12 ) 
+               << _boundaries[i] << '\n';
+        }
+
+        return ss.str();
+    }
+
+    uint64_t Histogram::getCount( uint32_t bucket ) const {
+        if ( bucket >= _numBuckets ) return 0;
+
+        return _buckets[ bucket ];
+    }
+
+    uint32_t Histogram::getBoundary( uint32_t bucket ) const {
+        if ( bucket >= _numBuckets ) return 0;
+
+        return _boundaries[ bucket ];
+    }
+
+    uint32_t Histogram::getBucketsNum() const {
+        return _numBuckets;
+    }
+
+    uint32_t Histogram::findBucket( uint32_t element ) const{
+        // TODO assert not too small a value?
+
+        uint32_t low = 0;
+        uint32_t high = _numBuckets - 1;
+        while ( low < high ){
+            // low + ( (high - low) / 2 );
+            uint32_t mid = ( low + high ) >> 1;
+            if ( element > _boundaries[ mid ] ){
+                low = mid + 1;
+            } else {
+                high = mid;
+            }
+        }
+        return low;
+    }        
+
+}  // namespace mongo